Thread: how to know which function belongs to which library?

as the title states..
what is the best way to know which function call belongs to which library?

I was coding in C and using GCC 4.x..
I know how to use System V IPC semaphores..
but I wanted to learn POSIX semaphores..
so i went through some internet tutorials and from manpages I could learn..
but I have no idea which library to link with my object file,
for my code to run.. I searched and searched.. after a long time I found it..
its like '-lrt'.. (no tute specified which lib to link )

so my question is in general how can one find the library to reference?
if I am stuck at such point.. man pages dont tell me which lib does this belong to..
they only tell me the header files..

I found some thread 2 years old on a forum asking to grep on /usr/lib/*
I did it and ended up with lot many results saying few matches found..
and one of them is libgc.. I didnt understand why I should be linking if its in libgc..
Also that grep didnt list 'librt'

can anyone help me?

Originally Posted by robwhit

it's in man pthreads. it's -lpthread.

thanks..
I thought it was only a posix thread lib..
still which is the actual lib for posix IPC functions?

do you have any idea about my original prob?

Originally Posted by ssharish2005

I tend to get most of the linker flag names from their man page. Most of them tent to have it in their. But some dont.

ssharish

lol..
thats what I was doing
but I tried something like
-lpsem
-lposix
-lps
-lsem
-lsema
-lsemaphores
-lmut
-lmutex
etc

but the actual name was -lrt.. I have no clue why it is so..
may be it is meant for ppl who know which lib are you going to use and not which header followed by lib..
still there might be some elegant way to find it out..
else google is for free .. or Brows LSB..

Originally Posted by robwhit

yeah I was wrong. This page seems to agree with you:

http://linux.die.net/man/7/mq_overview

no prob.. may be that -lrt is not so famous..
I found on some mailing lists that -lrt got some problem with pthread..
(it was 3-4 years old message)
and was advised to used pthread for semaphores..

and after that found some proff's homepage yelling in red color to compile it with -lrt

If you just do a 'grep' on libraries, you find where the symbols are unresolved as well as defined.

If you want to find where a symbol is defined, then use this approach, then pipe through grep

Code:

$ nm --defined-only /usr/lib/lib*.a | more

/usr/lib/libautomode.a:

automode.o:
00000000 b .bss
00000000 d .data
00000000 r .rdata
00000000 t .text
00000000 T _cygwin_premain0
00000000 d pf.0

/usr/lib/libbfd.a:

archive.o:
00000000 b .bss
00000000 d .data
00000000 r .rdata
00000000 t .text
000000a8 r __PRETTY_FUNCTION__.0
000001e0 T __bfd_add_bfd_to_archive_cache
00000000 T __bfd_ar_spacepad

It lists the name of each library and each public symbol which can be found in that library.

Originally Posted by Salem

If you just do a 'grep' on libraries, you find where the symbols are unresolved as well as defined.

If you want to find where a symbol is defined, then use this approach, then pipe through grep

Code:

$ nm --defined-only /usr/lib/lib*.a | more

/usr/lib/libautomode.a:

automode.o:
00000000 b .bss
00000000 d .data
00000000 r .rdata
00000000 t .text
00000000 T _cygwin_premain0
00000000 d pf.0

/usr/lib/libbfd.a:

archive.o:
00000000 b .bss
00000000 d .data
00000000 r .rdata
00000000 t .text
000000a8 r __PRETTY_FUNCTION__.0
000001e0 T __bfd_add_bfd_to_archive_cache
00000000 T __bfd_ar_spacepad

It lists the name of each library and each public symbol which can be found in that library.

wont this work for .so?